Amphiphilic Janus particles are biphasic colloids that have two sides with distinct chemistry and wettability. Because of their amphiphilicity, Janus particles have particular utility with respect to stabilizing multiphasic fluid mixtures such as emulsions. Studies have shown that Janus particles offer advantages over their homogenous counterparts as solid surfactants. For example, the adsorption energy of a spherical Janus particle to an oil-water (OW) interface can be as large as three times that of its homogenous counterpart. Thus, Janus particles have a strong tendency to segregate to and remain at fluid interfaces.
The behavior and function of Janus particles as surface active agents may depend upon the shape of the Janus particles as well as their amphiphilicity. Certain amphiphilic particles can change their shape and amphiphilicity in response to external stimuli such as temperature, pH and light, which in turn change the particles' properties and functionality as surface active agents. The so-called stimuli-responsive amphiphilic particles described in previous studies have limited ranges of amphiphilicity- and shape-tunability and, thus, cannot be used for inducing phase inversion of emulsions or for stabilizing different types of emulsions.
Thus, it would be useful to provide pH-responsive Janus particles that can switch their amphiphilicity due to changes in shape and chemistry. There is also a need for a Janus particle that may be used to stabilize different types of multiphasic mixtures. Further, it would be desirable to provide an amphiphilic particle that may also be used to induce a phase inversion of multiphasic mixtures in response to changes in the pH of the aqueous layer. It would also be desirable to provide an amphiphilic particle that may be used to induce a phase inversion of multiphasic mixtures in response to changes in the volume fraction of a component phase of the mixtures. Additionally, it would be desirable to provide a method by which both amphiphilic Janus particles and general anisotropic particles for stabilizing emulsions can be generated. Finally, it would be desirable to provide a pH-responsive Janus particle which permits adjustment of the interactions between oil-in-water emulsion droplets without inducing destabilization.